Musnad Ahmad 30:1460

'Affan narrated to us, Aban narrated to us, Yahya ibn Abi Kathir narrated to us, he said: Abu Ja'far narrated to me, from Abu Hurairah, that the Prophet of Allah, may Allah bless him and grant him peace, used to say: "Three supplications are answered, there is no doubt in them: the supplication of the oppressed, the supplication of the traveler, and the supplication of the parent against their child."